Until the 1950's, the effect of physical stresses on the musculoskeletal system were not given rigorous attention. Along with heightened awareness of the dependence of the musculoskeletal system on mechanical stresses, came new development in internal fixation, which permitted a revolution in orthopedic and therapeutic strategies. A majority of studies have concentrated on the remodeling processes of tissues and it has been found that lack of mechanical stimulation have adverse effects on tissues. Although one can infer that the application of mechanical loads would possibly affect tissue remodeling processes, the actual mechanisms underlying the effects of mechanical stimulation on tissues are not yet fully understood. The goal of this proposal is to elucidate the molecular and cellular responses of anterior cruciate ligament (ACL) and medial collateral ligament (MCL) fibroblasts and ACL/MCL tissues to mechanical stimuli. These responses may be significantly affected by perturbations in mechanical stimulations. The long-term goals are to gain insights on methods to promote proper healing of the ACL and enhance the healing rate of the MCL, as well as to develop a reconstructed ligament that has similar functions as its pre-injury state. The applicant's hypothesis is that mechanical stimulation of ACL/MCL cells promote the maintenance of tissue integrity and strength by influencing gene expression and the deposition and destruction of matrix by ligament cells. The following four Specific Aims will be pursued to test this hypothesis: (1) to determine the effects of mechanical stimuli (amplitude and frequency) on specific cellular processes, including proliferation, apoptosis, integrin response, and in vitro wound recovery; (2) to elucidate how mechanical stimuli regulate mechanisms of anabolic (types I and III collagen and fibronectin) and catabolic (MMP-I, MMP-III, TIMP-I), gene expression by ligament fibroblasts cultured in monolayers; and (3) to investigate the effects of mechanical stimuli on expression of anabolic and catabolic genes by ligament fibroblasts and intact tissue (bone-ligament-bone preparations).